I too will abandon a purchasing quest if they force that crap on me. Doubly so for all those small time sites that make me then log in or add something to my cart just to see a price.
I don't understand how this behaviour can persist when it's customer repellant. (Unless they're optimizing for a different captive market, and really aren't interested in my business).
Sometimes the "add to cart to see price" means you're getting a good price - the manufacturer set a minimum price and they're going below, and they don't want it to show up in searches.
Sometimes, at least, the 'add to cart for price' is done because the manufacturer or distributor of products will forbid retailers from advertising lower prices on their site. When I worked in an industry that had these policies enforced, the reasoning we were given was that the policy was in place to maintain healthy competition between retailers selling the same products.
It's repellant for signups, but it's positive that once a customer does sign up, you keep marketing to them for long-term value and future purchases.
The other answer is you optimize for what you can measure. It's hard to know when users are dropping off at the account-signup wall; it's easy to know when an existing user bites on your re-marketing efforts.
I don't understand how this behaviour can persist when it's customer repellant. (Unless they're optimizing for a different captive market, and really aren't interested in my business).